Syntheses of Segmental Heteroleptic Ligands for the Self-Assembly of Heteronuclear Helical Supramolecular Complexes

The development of a modified Phillips reaction allows the synthesis of complicated heteroleptic ligands based on pyridine and 1H-benzimidazole moieties. The key-step formation of aromatic 1H-benzimidazole rings from N-(2-nitroaryl)arenecarboxamides significantly improves the possibilities of the classical intermolecular Phillips reactions and can be applied to the synthesis of large oligo-multidentate units. Segmental heteroleptic ligands containing two different bidentate coordinating units (see 14) or bidentate and terdentate sites connected by ‘diphenylmethane’ ( = methylenebis(phenylene)) spacers (see 15 and 16) were obtained in fair to good yield by using multistep syntheses following this strategy. Heterotrileptic ligands (bidentate-terdentate-bidentate, see 19 and 20; terdentate-terdentate-terdentate, see 23) requiring the simultaneous formation of four 1H-benzimidazole rings in one step were prepared and demonstrate the extended possibilities of this methodology. Data are presented to show that the milder conditions used for this modified Phillips reaction together with its flexibility are essential for the development of ligands adapted for the self-assembly of heteronuclear helical complexes.